In recent years, various kinds of notebook-type or laptop-type portable personal computers have been developed. In the field of portable personal computers, there has been a demand for achieving power saving of such computers.
To meet this demand, recently, a computer having a function of powering off a device within the computer, where necessary, has been developed. By powering off the device, the power consumption of the computer can be reduced.
However, at a time of starting the use of the device, for example, a user himself/herself has to perform an operation of powering on the device. If an application program which uses a certain device is started in the state in which the device is powered off, it is possible that this application program cannot normally operate.
In addition, there is known a technique wherein a device driver which controls a specific device detects the start and termination of a purpose-specific application program which uses this specific device, and thereby the state of the specific device is switched between an operation mode and a power-save mode.
In general, however, in a computer, the relationship between a device and an application program which uses the device is not always a one-to-one correspondence. Depending on an application program which is started, the device which is used by this application program may differ. Besides, a certain device may be used by some application programs.